Since the release, I've soloed arenas on all three tiers, doing all 3 parts of each arena. The gun puppy phases are harder than they were, but were no where near the hardest part. Yes, you have to stand a ways away from them while charging up your sword rather than directly behind them, but that is very minor. Yes, you can't run past them to escape monsters from previous waves, but that just means you need to be careful to keep the waves under control.
i'll take the current gun puppies over the phase with the giant lichen colony charging around plus four alpha wolvers plus 2 T3 gremlin healers that are happy to resurrect each other.
haven't tried an arena with the new puppy-set buuuut... managed to encounter this for the first time slightly before the patch
http://i.imgur.com/154RE.jpg
what i had equipped at the time was an ascended calibur, avenger and a freezing vaporizer
now that was tough :D ...
and then the only reward after doing so was a bit of heat and a potion =(